1. Field of the Invention
The present invention relates to a trench structure and method of forming the same. More particularly, the present invention relates to a trench structure for the isolation of a semiconductor device and a method of forming the same.
2. Description of the Related Art
Because semiconductor devices are being developed to have high integration densities, a method of isolating semiconductor devices with excellent insulation characteristics in a minute area of the semiconductor device is required. Generally, isolation of semiconductor devices is achieved by a local oxidation of silicon (LOCOS) process or a trench isolation process.
Good semiconductor device isolation characteristics may be obtained simply with the LOCOS process. However, the LOCOS process requires a wider isolation area than the trench isolation process, and defects such as a bird's beak commonly occur during the LOCOS process. Thus, the trench isolation process is widely used for the isolation of semiconductor devices.
In the trench isolation process, a trench is formed in a substrate using a nitride film as an etching mask. Then, the trench is filled with a filling insulation material such as an oxide. Finally, a chemical-mechanical polishing (CMP) process is performed for forming a trench structure.
According to the prior art, a trench isolation method may include isolating a semiconductor device in a trench by forming a trench structure in a substrate and successively forming a thermal oxidation film, a chemical vapor deposition (CVD) oxide film, a liner layer and an insulation film in the trench in order to minimize the generation of a dent in the substrate.
In addition, there is known in the art a method of successively forming a thermal oxidation film, an insulation oxide film, a liner layer and an insulation film for the isolation of a semiconductor device in a trench when a trench structure is formed in a substrate in order to reduce parasitic leakage and hot carrier degradation.
The methods described above for forming a trench structure provide good isolation properties. However, although the trench structure has excellent isolation characteristics, a void is frequently generated in a trench when the trench structure is formed. In particular, voids are more frequently and acutely generated when trench structures are continuously formed in trenches having different aspect ratios.
FIG. 1 illustrates a cross-sectional view showing trench structures formed according to a conventional method. In FIG. 1, a substrate 10 is divided into a cell region, where devices such as trench structures are formed, and a peripheral region, where a connection wiring for the devices in the cell region is positioned.
Referring to FIG. 1, a trench 14a in the cell region has an aspect ratio different from an aspect ratio of a trench 14b in the peripheral region. In this case, the aspect ratio of the trench 14a in the cell region is twice that of the trench 14b in the peripheral region. When the trench structure is formed, however, the trench 14a in the cell region has a structure that is identical to that of the trench 14b in the peripheral region. That is, a filling structure 12a that fills the trench 14a in the cell region has a structure identical to that of a filling structure 12b that fills the trench 14b in the peripheral region. A void 16 is frequently generated in the trench structure in the cell region because identical filling structures 12a and 12b are used to fill the trenches 14a and 14b even though the trenches 14a and 14b have different aspect ratios. FIG. 1 illustrates the previously described condition of frequent void generation in trench structures occurring when the trench structures are continuously formed in cell and peripheral regions of a substrate. Such generation of voids may result in the deterioration of the semiconductor device operating characteristics. Hence, it is greatly required that a trench structure for semiconductor device isolation be formed without the generation of voids therein.